A network engineer wants to ensure that all network devices in a branch office synchronize their clocks with the corporate NTP server located at 10.1.1.1, which operates in stratum 3. The branch office router should act as an NTP client to the corporate server and then serve as an NTP authoritative server for other devices in the branch, but only if it successfully synchronizes with the corporate server. Which command sequence achieves this goal?
- ARouter(config)# ntp server 10.1.1.1 Router(config)# ntp master
- BRouter(config)# ntp server 10.1.1.1 Router(config)# ntp master 4
- CRouter(config)# ntp server 10.1.1.1 Router(config)# ntp peer 10.1.1.1
- DRouter(config)# ntp server 10.1.1.1 prefer Router(config)# ntp master 8
Show answer & explanationAnswer & explanation
Correct answer: B. Router(config)# ntp server 10.1.1.1 Router(config)# ntp master 4
The 'ntp server 10.1.1.1' command configures the router as an NTP client to the corporate server. The 'ntp master [stratum]' command makes the router an authoritative NTP server, but critically, if it has successfully synchronized with an external source (like the corporate server), it will use its stratum plus one (e.g., 3+1=4). If it cannot synchronize, it will use the configured stratum (e.g., 4) itself. This setup ensures it only acts as an authoritative source if synchronized or if no other source is available at the specified stratum.
Why the other options are wrong
- A. The 'ntp master' command without a stratum uses a default stratum of 8, which might be too high (less accurate) for the requirement of serving a synchronized time based on a stratum 3 source. The question implies it should be authoritative based on its synchronization, which would typically be one stratum higher than its source (3+1=4).
- C. The 'ntp peer' command is for two-way communication between servers, typically for redundancy, not for a client-server then master scenario.
- D. The 'prefer' keyword is for multiple servers but doesn't change the master behavior. 'ntp master 8' would make it a lower-priority master than required, and 'prefer' is not necessary for a single server.
NTP Master Command
The 'ntp master [stratum]' command configures a router to act as an authoritative NTP server, using the specified stratum if it cannot synchronize with an external source, or its synchronized source's stratum plus one if it can.
- Makes router an authoritative NTP server.
- Stratum value (1-15) indicates accuracy/distance from primary source.
- Router's stratum becomes (source stratum + 1) if synchronized, else uses configured master stratum.
Memory trick: An NTP Master acts as a time 'godfather' for its local network, but only if it trusts a higher-up 'don' (corporate server).